A Question of Which Book

[buvuturo]

No: HPFGUIDX 144834

In the US paperback edition of POA, Chapter 14, page 285, paragraph 2,
Harry finally snaps and tells Snape to shut up about his father.  He
says that Dumbledore has told him the truth: that James Potter saved
Snape's life, and Snape wouldn't even be there if not for his father.

Paragraphs 4 and 6 are Snape's response, wherein he states that most
likely Dumbledore hadn't told the full story, out of concern for
Harry's delicate sensabilities.  He says that there was nothing of
bravery or glory in it, that James did it solely to save his own skin,
since he would have been expelled if the deadly prank had been allowed
to complete itself and result in Snape's death.

My question is, where does Dumbledore tell Harry about the origin of
"Snape's Grudge"(as the POA chapter is named)?  

Which book is it in?  I've wanted to refer back to it, only to find it
eluding me.

Thanks for any assistance.

Bianca